System and Method for Selecting a Number of Spatial Streams to Be Used for Transmission Based on Probing of Channels

1. A method, comprising: generating a Probability of Channel non-Correlation (PCC) function at a source node that indicates a probability of whether a plurality of spatial channels are non-correlated based on feedback from a destination node; determining a packet size of a data packet to be transmitted by the source node when the source node prepares to transmit the data packet, wherein the data packet comprises symbols; determining, at a source node before the source node transmits the data packet to the destination node, whether a packet size of the data packet is greater than a packet size threshold; and determining, at the source node when the packet size of the data packet is less than or equal to the packet size threshold, whether a current value of the PCC function is greater than a first threshold; when the current value of the PCC function is greater than the first threshold: selecting, at the source node, a plurality of non-correlated spatial channels to be used for transmission of the data packet to the destination node, and transmitting symbols of the data packet from a plurality of different antennas as a plurality of spatial streams over the plurality of non-correlated spatial channels.

2. A method according to claim 1 , further comprising: selecting, at the source node, a single one of the spatial channels to be used for transmission of the data packet to the destination node when the current value of the PCC function is less than or equal to the first threshold, and transmitting the symbols of data packet from a single antenna of the source node as a single stream over the single spatial channel.

3. A method according to claim 1 , when the packet size of the data packet is greater than the packet size threshold, further comprising: determining, at the source node based on a current value of the PCC function, whether to transmit a probe packet; transmitting symbols of the probe packet, from the source node to the destination node, via a plurality of spatial streams over a plurality of spatial channels to generate a data point that characterizes the likelihood of channel non-correlation; determining, at the source node, whether a probe acknowledgement (ACK) message was received to determine a number of spatial streams to be used for transmission of the data packet; transmitting symbols of the data packet, from the source node to the destination node, from the plurality of different antennas as a plurality of spatial streams over a plurality of non-correlated spatial channels when the source node determines that a probe ACK message was received, and transmitting symbols of the data packet, from the source node to the destination node, from the single antenna of the source node as a single stream over the single spatial channel when the source node determines that a probe ACK message was not received.

4. A method according to claim 3 , wherein determining, at the source node based on a current value of the PCC function, whether to transmit a probe packet comprises: determining, at the source node, whether a current value of the PCC function is greater than an upper PCC threshold; when the source node determines that the current value of the PCC function is greater than the upper PCC threshold, randomly determining, at the source node, whether probing is required based on evaluation of a first probability function (PCC) that that provides a general measure of channel non-correlation and biases the probability of whether a probe packet will be transmitted; and transmitting, from the source node, symbols of the probe packet over a plurality of spatial channels to the destination node when the source node determines that probing is required based on evaluation of the first probability function (PCC).

5. A method according to claim 4 , further comprising: transmitting symbols of the data packet, from the source node to the destination node, from the plurality of different antennas as a plurality of spatial streams over a plurality of non-correlated spatial channels when the source node determines that probing is not required based on evaluation of the first probability function (PCC).

6. A method according to claim 3 , wherein the step of determining, at the source node based on a current value of the PCC function, whether to transmit a probe packet, further comprises: determining, at the source node, whether a current value of the PCC function is greater than an upper PCC threshold; when the source node determines that the current value of the PCC function is less than or equal to the upper PCC threshold, determining, at the source node, whether the current value of the PCC function is greater than a lower PCC threshold; when the source node determines that the current value of the PCC function is less than or equal to the lower PCC threshold, randomly determining, at the source node, whether probing is required based on evaluation of a second probability function (1-PCC) that provides a general measure of channel correlation and biases the probability of whether a probe packet will be transmitted; transmitting, from the source node, symbols of the probe packet over a plurality of spatial channels to the destination node when the source node determines that probing is required based on evaluation of the second probability function (1-PCC).

7. A method according to claim 6 , further comprising: transmitting symbols of the data packet, from the source node to the destination node, from the plurality of different antennas as a plurality of spatial streams over the plurality of non-correlated spatial channels when the source node determines that probing is not required based on evaluation of the second probability function (1-PCC).

8. A method according to claim 6 , further comprising: transmitting, from the source node, symbols of the probe packet over a plurality of spatial channels to the destination node when the source node determines that the current value of the PCC function is greater than the lower PCC threshold.

9. A method according to claim 1 , further comprising: receiving, at the source node, a data packet acknowledgement (ACK) message; and updating the PCC function at the source node when a data packet ACK message is received.

10. A method according to claim 9 , further comprising: starting an acknowledgement (ACK) timer at the source node that specifies a timeout period upon transmitting symbols of the data packet.

11. A method according to claim 10 , wherein updating the PCC function at the source node when a data packet ACK message is received, comprises: determining, at the destination node, whether symbols of the data packet are successfully received at a plurality of different antennas of the destination node; and transmitting, from the destination node, a data packet acknowledgement (ACK) message when the packet was successfully received by the destination node to provide explicit feedback that the transmission over the plurality of spatial streams was successful; determining, at the source node after the timeout period expires, whether the data packet ACK message was received; determining, at the source node when the data packet ACK message was not received at the source node within the timeout period, that the plurality of spatial channels are correlated as transmission of the plurality of spatial streams was unsuccessful, and generating a new data point that is used to update the PCC function, where the new data point represents that the plurality of spatial channels are correlated at a particular instant in time; determining, at the source node when the data packet ACK message was received at the source node within the timeout period, that the plurality of spatial channels are non-correlated as transmission of the plurality of spatial streams was successful, and generating a new data point that is used to update the PCC function, where the new data point represents that the plurality of spatial channels are non-correlated at a particular instant in time; and updating, at the source node, the PCC function based on a moving average of the new data point and a number of prior data points to indicate a probability that characterizes a likelihood of whether the plurality of spatial channels are non-correlated.

12. A method according to claim 11 , further comprising: repeating the operations of claim 11 each time a new data packet is transmitted by the source node.

13. A method according to claim 1 , wherein determining a packet size of a data packet to be transmitted by the source node, comprises: selecting, at the source node, a modulation scheme, a forward error correction (FEC) scheme and a date rate to be used for transmission of a data packet when the source node prepares to transmit the data packet; and determining a packet size of the data packet based on the modulation scheme, the FEC scheme and the date rate.

14. A method according to claim 1 , wherein the current value of the PCC function being greater than the first threshold implies that the plurality of non-correlated spaital channels are available for communication with the destination node, and wherein the current value of the PCC function being less than or equal to the first threshold implies that the number of spaital channels for communication with the destination node are correlated.

15. A method according to claim 1 , wherein the plurality of spatial streams comprise two spatial streams and wherein the plurality of non-correlated spatial channels comprise two non-correlated spatial channels, and wherein determining whether a current value of the PCC function is greater than a first threshold comprises: determining, at the source node when the packet size of the data packet is less than or equal to the packet size threshold, whether a current value of the PCC function is greater than a first threshold to determine whether the data packet is to be transmitted using one stream or two spatial streams; and wherein transmitting symbols of the data packet from the plurality of different antennas as the plurality of spatial streams over the plurality of non-correlated spatial channels comprises: transmitting symbols of the data packet to the destination node from two different antennas as two spatial streams over the two non-correlated spatial channels when the current value of the PCC function is determined to be greater than the first threshold.

16. A method according to claim 1 , wherein the source node and the destination node are multiple input multiple output (MIMO) enabled, and wherein the source node and the destination node both include multiple antennas.

17. A method according to claim 1 , wherein generating a Probability of Channel non-Correlation (PCC) function at the source node further comprises: transmitting the data packet from the source node and starting an acknowledgement (ACK) timer; determining, at the source node upon expiration of the ACK timer, whether a data packet acknowledgement (ACK) message was received by the source node; and updating the PCC function at the source node based on whether the data packet ACK message was received.

18. A method according to claim 17 , further comprising: determining, at the destination node, whether symbols of the data packet are successfully received at a plurality of different antennas of the destination node; transmitting, from the destination node, a data packet acknowledgement (ACK) message when the packet was successfully received by the destination node to provide explicit feedback that the transmission over the plurality of spatial streams was successful; determining, at the source node after the timeout period expires, whether the data packet ACK message was received; determining, at the source node when the data packet ACK message was not received at the source node within the timeout period, that the plurality of spatial channels are correlated as transmission of the plurality of spatial streams was unsuccessful, and generating a new data point that is used to update the PCC function, where the new data point represents that the plurality of spatial channels are correlated at a particular instant in time; determining, at the source node when the data packet ACK message was received at the source node within the timeout period, that the plurality of spatial channels are non-correlated as transmission of the plurality of spatial streams was successful, and generating a new data point that is used to update the PCC function, where the new data point represents that the plurality of spatial channels are non-correlated at a particular instant in time; and wherein the step of updating the PCC function at the source node based on whether the data packet ACK message was received, comprises: updating, at the source node, the PCC function based on a moving average of the new data point and a number of prior data points to indicate a probability that characterizes a likelihood of whether the plurality of spatial channels are non-correlated.

19. A method according to claim 18 , further comprising: repeating operations of claim 18 each time a new data packet is transmitted by the source node.

20. A method, comprising: generating a Probability of Channel non-Correlation (PCC) function at a source node that indicates a probability of whether a plurality of spatial channels are non-correlated based on feedback from a destination node; determining a packet size of a data packet to be transmitted by the source node when the source node prepares to transmit the data packet, wherein the data packet comprises symbols; determining, at a source node before the source node transmits the data packet to the destination node, whether a packet size of the data packet is greater than a packet size threshold; when the packet size of the data packet is greater than the packet size threshold, determining, at the source node based on a current value of the PCC function, whether to transmit a probe packet; and transmitting symbols of the probe packet, from the source node to the destination node, via a plurality of spatial streams over a plurality of spatial channels to generate a data point that characterizes the likelihood of channel non-correlation.

21. A method according to claim 20 , further comprising: determining, at the source node, whether a probe acknowledgement (ACK) message was received to determine a number of spatial streams to be used for transmission of the data packet; and transmitting symbols of the data packet, from the source node to the destination node, from a plurality of different antennas as a plurality of spatial streams over a plurality of non-correlated spatial channels when the source node determines that a probe ACK message was received.

22. A method according to claim 20 , further comprising: transmitting symbols of the data packet, from the source node to the destination node, from a single antenna of the source node as a single stream over the single spatial channel when the source node determines that a probe ACK message was not received.

23. A method according to claim 20 , further comprising: determining, at the source node when the packet size of the data packet is less than or equal to the packet size threshold, whether a current value of the PCC function is greater than a first threshold; selecting, at the source node, plurality of non-correlated spatial channels to be used for transmission of the data packet to the destination node when the current value of the PCC function is greater than the first threshold; and transmitting symbols of the data packet from a plurality of different antennas as a plurality of spatial streams over a plurality of non-correlated spatial channels, wherein the current value of the PCC function being greater than the first threshold implies that the plurality of non-correlated spaital channels are available for communication with the destination node.

24. A method according to claim 23 , further comprising: selecting, at the source node, a single one of the spatial channels to be used for transmission of the data packet to the destination node when the current value of the PCC function is less than or equal to the first threshold; and transmitting the symbols of data packet from a single antenna of the source node as a single stream over the single spatial channel, wherein the current value of the PCC function being less than or equal to the first threshold implies that the number of spaital channels for communication with the destination node are correlated.

25. A method according to claim 20 , wherein determining, at the source node based on a current value of the PCC function, whether to transmit a probe packet comprises: determining, at the source node, whether a current value of the PCC function is greater than an upper PCC threshold; when the source node determines that the current value of the PCC function is greater than the upper PCC threshold, randomly determining, at the source node, whether probing is required based on evaluation of a first probability function (PCC) that that provides a general measure of channel non-correlation and biases the probability of whether a probe packet will be transmitted; and transmitting, from the source node, symbols of the probe packet over a plurality of spatial channels to the destination node when the source node determines that probing is required based on evaluation of the first probability function (PCC).

26. A method according to claim 25 , further comprising: transmitting symbols of the data packet, from the source node to the destination node, from the plurality of different antennas as a plurality of spatial streams over a plurality of non-correlated spatial channels when the source node determines that probing is not required based on evaluation of the first probability function (PCC).

27. A method according to claim 26 , wherein determining, at the source node based on a current value of the PCC function, whether to transmit a probe packet, further comprises: determining, at the source node, whether a current value of the PCC function is greater than an upper PCC threshold; when the source node determines that the current value of the PCC function is less than or equal to the upper PCC threshold, determining, at the source node, whether the current value of the PCC function is greater than a lower PCC threshold; when the source node determines that the current value of the PCC function is less than or equal to the lower PCC threshold, randomly determining, at the source node, whether probing is required based on evaluation of a second probability function (1-PCC) that provides a general measure of channel correlation and biases the probability of whether a probe packet will be transmitted; and transmitting, from the source node, symbols of the probe packet over a plurality of spatial channels to the destination node when the source node determines that probing is required based on evaluation of the second probability function (1-PCC).

28. A method according to claim 27 , further comprising: transmitting symbols of the data packet, from the source node to the destination node, from the plurality of different antennas as a plurality of spatial streams over the plurality of non-correlated spatial channels when the source node determines that probing is not required based on evaluation of the second probability function (1-PCC).

29. A method according to claim 27 , further comprising: transmitting, from the source node, symbols of the probe packet over a plurality of spatial channels to the destination node when the source node determines that the current value of the PCC function is greater than the lower PCC threshold.

30. A method according to claim 20 , further comprising: receiving, at the source node, a data packet acknowledgement (ACK) message; and updating the PCC function at the source node when a data packet ACK message is received.